Presidential hopeful Herman Cain stops by Detroit

That plan has come under attack for being unfair to lower-income people. But Cain says it has provisions for economically distressed cities like Detroit.

Cain says his 9-9-9 plan would help rejuvenate the economy, which he says is “on life support.” Each “nine” stands for a new policy: a 9 percent federal flat tax, a 9 percent national sales tax, and a 9 percent national business tax.

But, Cain says the plan would make an exception for the poorest Americans: the 9-0-9.

“In other words, if you are at or below the poverty level, then you don’t pay that middle nine tax on your income,” Cain said. “This is how we help the poor.”

That set-up would allow different groups to submit plans identifying and eliminating cumbersome regulations, and other policies that squash economic growth.

Cain stood in front of Detroit’s abandoned train depot to make a point about what he calls “failed liberal policies,” particularly high taxes and excessive government regulation. He said eliminating taxes like the capital gains tax will help spur investment in blighted areas.

“What if an investor wanted to do something with this building behind us?" Cain asked. "What if they wanted to spend $10 m to turn it into a mall or a restaurant facility? Under 999, they would be able to deduct that capital investment in the year that they make it.”

Cain later said he was unaware that the empty building is owned by billionaire Ambassador Bridge owner Manuel Moroun.